We have continued to explore the mechanism of action of intravenous immunoglobulin in reducing autoimmune damage. During this year it was shown that intravenous immunoglobulin does not reduce the amount of C1 bound to targets. However, it does reduce the amount of C4 and C3 bound to targets equally. Preliminary data suggest that C3 binding is not the primary target of intravenous immunoglobulin but that C4 is more important. The actual mechanism of action of the intravenous immunoglobulin and the structural correlates of the target are under investigation.